Thenaria (Endomyaria) the base of which forms a float. It is hollowed out and has indrawn edges with only a slight opening (abnormally two), the cavity being filled by a chitinuous [sic], porous mass. Sphincter circumscribed. Tentacles simple or branched, arranged in radial series over the endocoels as from the exocoels. In very young specimens the arrangement of tentacles in rows is not conspicuous. Arrangement of mesenteries curious owing to the strong enlargement of the endocoels and strong diminution of the exocoels.
Definitions and contained taxa are those of Oscar Carlgren as published in 1949 : Kungl Svenska Vetenskapsakadamiens Handlingar, Series 4, Volume 1, Number 1